Prehistoric Parasites from the Silurian

Rare Discovery Provides Insight into Ancient Parasite

A team of international researchers have got up close to a prehistoric parasite, one that is perfectly preserved along with its 425 million-year-old host. The ancient parasite, known as a “tongue worm” provides scientists with a glimpse of life and the interactions between species in a warm tropical sea that existed in Britain back in the Middle Silurian. Fossils of tongue worms are extremely rare, examples have been recovered from Ordovician as well as older Cambrian deposits, the Silurian fossils are exceptionally well preserved, we at Everything Dinosaur believe the fossils to be part of the Wenlock Epoch biota. The actual location of the fossil find has not been disclosed in order to protect the site from amateur fossil hunters and those keen to exploit the fossil deposits commercially.

The fossils come from a deposit in Herefordshire, close to the border with Wales, scientists from the University of Leicester, who took part in the study stated that the tongue worm represents a new species and they range in size from 1mm to 4mm in length. Tongue worms have tongue shaped bodies, a distinct head and two pairs of limbs. At least 140 species are known to exist today, most are respiratory or gut parasites of vertebrates (usually reptiles), these fossils provide scientists with information on how these creatures evolved before they made the move onto land to become parasites of terrestrial vertebrates.

The picture above shows the pentastomid Invavita piratica and its host, the Ostracod Nymphatelina gravida.

The newly described fossils show the tongue worm species in association with its host, in this case a species of Ostracod (an Arthropod). It was professor David Siveter, (Department of Geology) at Leicester University, who made the discovery. An academic paper describing the new species, named as Invavita piratica, (the name translates as ancient, pirate intruder) has been published in the journal “Current Biology”. As well as academics from the University of Leicester, the research team included scientists from Imperial College (London), Oxford University and Yale. Tongue worms belong to the Pentastomida Family, part of the Subphylum Crustacea, although for many years the taxonomic relationship between this group of obligate parasites and other parts of the Arthropoda was disputed.

Professor Siveter, explained that the tongue worms were not “worms” at all, they got their name because one genus resembles the tongue of an animal. They are an unusual and widespread group of mainly obligate parasites. An obligate parasite is an organism that cannot complete its life-cycle without finding a suitable host.

The professor stated:

“This discovery affirms that tongue worms were “external” parasites on marine invertebrates animals at least 425 million years ago. It also suggests that tongue worms likely found their way into land-based environments and associated hosts in parallel with the movement of vertebrates onto the land by some 125 million years later.”

The Computer Model with the Ostracod Shell Removed to Reveal the Internal Parasites

Internal parasites identified by high powered scans and computer modelling.

Picture Credit: Siveter, Briggs, Siveter and Sutton

The computer image above shows the Ostracod with its shell removed, showing the external pentastomids and a pentastomid near the eggs of the Ostracod (parasites in orange). The picture shows how this group of parasites got their name. “Penta” refers to the number five and these parasites have five anterior appendages. One is the simple mouth, the others are two pairs of hooks which they use to attach themselves to their host. The large pentastomid (top left) is a highly magnified image of a single parasite, not to scale with the rest of the image.

Using sophisticated microscopic scanning techniques and three-dimensional computer modelling, the scientists were able to reconstruct the Ostracod and its parasites. Some of the tongue worms were found inside the Ostracod’s shell , near its eggs, on which they probably fed. Other tongue worms are attached to the external surface of the Ostracod’s shell, a unique position for any fossil or living tongue worm. These tiny fossilised creatures are helping the scientists to understand a little more about inter-relationships between parasites and potential hosts in ancient marine environments.

Back in 2012, Everything Dinosaur reported on the discovery of another ancient Ostracod from the same location. The fossil had been identified using the same techniques to discover the parasites. Professor Siveter, named this new genus of Ostracod after his wife.